Antiferromagnetic Type Research Articles

Asymptotic Behaviour of Ground States for Mixtures of Ferromagnetic and Antiferromagnetic Interactions in a Dilute Regime

We consider randomly distributed mixtures of bonds of ferromagnetic and antiferromagnetic type in a two-dimensional square lattice with probability $1-p$ and $p$, respectively, according to an i.i.d. random variable. We study minimizers of the corresponding nearest-neighbour spin energy on large domains in ${\mathbb Z}^2$. We prove that there exists $p_0$ such that for $p\le p_0$ such minimizers are characterized by a majority phase; i.e., they take identically the value $1$ or $-1$ except for small disconnected sets. A deterministic analogue is also proved.

Effect of Pressure on the Electronic, Magnetic, and Optical Properties of the In0.75Cr0.25P Compound

Using the density functional theory (DFT) approach and full-potential linearized augmented plane waves (FP-LAPW) method, some of the electronic (density of states, band structure, and Fermi surfaces), magnetic (total and local magnetic moments, spin polarization, exchange constants), and optical properties (dielectric function, energy loss function, and refractive index) were investigated. The GGA + U approximation was used for the exchange-correlation term. The effect of hydrostatic pressure up to 20 GP has been studied on these properties. The results show that the In0.75Cr0.25P compound is a half metal with 100% spin polarization at the Fermi level and the increment of pressure does not change its half-metallic behavior. The half-metal gap achieved for this compound is variable between 1.38 and 1.5 eV. The interaction between Cr and P atoms in this compound is an anti-ferromagnetic type. It was observed that the total magnetic moment for this compound is about 3 μB. Local magnetic moments change with increasing pressure, but the total magnetic moment remains unaffected by increasing the pressure. Calculations of the optical properties of the In0.75Cr0.25P compound showed that the dominant mechanism for the low-energy photons is due to the induced free carriers of the Cr atom, and the optical properties of this compound, in particular the refractive index in the visible region, change with increasing pressure.

Spin-liquid-like state in a spin-1/2 square-lattice antiferromagnet perovskite induced by d10\u2013d0 cation mixing

A quantum spin liquid state has long been predicted to arise in spin-1/2 Heisenberg square-lattice antiferromagnets at the boundary region between Néel (nearest-neighbor interaction dominates) and columnar (next-nearest-neighbor interaction dominates) antiferromagnetic order. However, there are no known compounds in this region. Here we use d10–d0 cation mixing to tune the magnetic interactions on the square lattice while simultaneously introducing disorder. We find spin-liquid-like behavior in the double perovskite Sr2Cu(Te0.5W0.5)O6, where the isostructural end phases Sr2CuTeO6 and Sr2CuWO6 are Néel and columnar type antiferromagnets, respectively. We show that magnetism in Sr2Cu(Te0.5W0.5)O6 is entirely dynamic down to 19 mK. Additionally, we observe at low temperatures for Sr2Cu(Te0.5W0.5)O6—similar to several spin liquid candidates—a plateau in muon spin relaxation rate and a strong T-linear dependence in specific heat. Our observations for Sr2Cu(Te0.5W0.5)O6 highlight the role of disorder in addition to magnetic frustration in spin liquid physics.

Electrical and Magnetic Properties of Hafnium Disulfide Intercalated with Iron Atoms

Simultaneous study of the dependences of the structural parameters, electrical, and magnetic properties of hafnium disulfide intercalated iron atoms in the dependence on the intercalate concentration and temperature has been performed for the first time. The temperature dependences of the electrical resistance are shown to exhibit the activation character with the activation energies characteristic of impurity conduction. The effective magnetic moments of iron ions in Fe x HfS2 is found to be significantly lesser than the values of free iron ions and to decrease as the iron content increases. The character of the temperature dependences of the effective magnetic moments and negative values of the paramagnetic Curie temperatures indicate possible interactions of the antiferromagnetic type between intercalated atoms. However, the dependences of the magnetization on field for Fe0.33HfS2 and Fe0.5HfS2 obtained at T = 2 K demonstrate the hysteresis phenomenon characteristic of the ferromagnetic state. The results are discussed assuming the existence of hybridization 3d electron states of intercalated iron atoms with the electronic states of HfS2 matrices and the competition of various exchange interaction.

Электрические и магнитные свойства дисульфида гафния, интеркалированного атомами железа

AbstractSimultaneous study of the dependences of the structural parameters, electrical, and magnetic properties of hafnium disulfide intercalated iron atoms in the dependence on the intercalate concentration and temperature has been performed for the first time. The temperature dependences of the electrical resistance are shown to exhibit the activation character with the activation energies characteristic of impurity conduction. The effective magnetic moments of iron ions in Fe_ x HfS_2 is found to be significantly lesser than the values of free iron ions and to decrease as the iron content increases. The character of the temperature dependences of the effective magnetic moments and negative values of the paramagnetic Curie temperatures indicate possible interactions of the antiferromagnetic type between intercalated atoms. However, the dependences of the magnetization on field for Fe_0.33HfS_2 and Fe_0.5HfS_2 obtained at T = 2 K demonstrate the hysteresis phenomenon characteristic of the ferromagnetic state. The results are discussed assuming the existence of hybridization 3 d electron states of intercalated iron atoms with the electronic states of HfS_2 matrices and the competition of various exchange interaction.

Magnetic interaction at the interface of epitaxial manganite film and (TbCo2/FeCo)n superlattice

Hybrid magnetic heterostructures made of epitaxial manganite La0.7Sr0.3MnO3 thin film and intermetallic superlattice (TeCo2/FeCo)n were prepared on orthorhombic NdGaO3 substrates and characterized by means of magneto-optical Kerr effect and magnetoresistance. Experimental data show that magnetic interaction between La0.7Sr0.3MnO3 and (TeCo2 /FeCo)n is of the antiferromagnetic type. The features observed in magnetotransport characteristics are caused by the magnetization reversal at the interface between manganite thin film and intermetallic superlattice.

Structure, magnetism and electronic properties in 3d–5d based double perovskite (Yx)2FeIrO6

The 3d–5d based double perovskites are of current interest as they provide model systems to study the interplay between electronic correlation (U) and spin–orbit coupling (SOC). Here, we report detailed structural, magnetic and transport properties of doped double perovskite material (Yx)2FeIrO6 with . With substitution of Y, the system retains its original crystal structure but structural parameters change with x in nonmonotonic fashion. The magnetization data for Sr2FeIrO6 show antiferromagnetic type magnetic transition around 45 K; however, a close inspection of the data indicates a weak magnetic phase transition around 120 K. No change of structural symmetry has been observed down to low temperature, although the lattice parameters show sudden changes around the magnetic transitions. Sr2FeIrO6 shows an insulating behavior over the whole temperature range, which nevertheless does not change with Y substitution. The nature of charge conduction is found to follow thermally activated Mott’s variable range hopping and power law behavior for parent and doped samples, respectively. Interestingly, evolution of structural, magnetic and transport behavior in (Yx)2FeIrO6 is observed to reverse with , which is believed to arise due to a change in the transition metal ionic state.

Switching of the exchange interaction character in the binuclear copper(II) complexes based on the hetaryl derivatives of 1,3-diaminopropanol-2

The binuclear copper(II) complex with bis-azomethine, viz., the product of condensation of 1,3-diaminopropanol-2 with 4-hydroxy-3-formylcoumarin (H3L), of the composition [Cu2L(μ2-CH3COO)] (I) is synthesized and studied. Complex I is characterized by the exchange interaction of the antiferromagnetic type (2J =–112 cm–1), which is switched to the ferromagnetic one (2J = +106 cm–1) after the recrystallization of the complex from dimethyl sulfoxide (DMSO) to form solvate [Cu2L(μ2-CH3COO)(μ2-DMSO)] · 0.5DMSO (II). The structure of solvate II is studied by X-ray diffraction analysis (CIF file CCDC no. 982198). The difference in the exchange character is explained by the stabilization by the μ2-coordinated DMSO molecule of a distorted (roof-shaped type) conformation of the polydentate ligand and the complex as a whole, unlike the symmetric conformation characteristic of the nonsolvated complex. The data obtained are compared with those on similar compounds synthesized earlier and with the quantum chemical modeling results for the exchange interaction in the framework of the DFT-BS approximation.

Channel-Assisted Proton Conduction Behavior in Hydroxyl-Rich Lanthanide-Based Magnetic Metal-Organic Frameworks.

Two new lanthanide-based 3D metal-organic frameworks (MOFs), {[Ln(L)(Ox)(H2O)]n·xH2O} [Ln = Gd3+ and x = 3 (1) and Dy3+ and x = 1.5 (2); H2L = mucic acid; OxH2 = oxalic acid] showing interesting magnetic properties and channel-mediated proton conduction behavior, are presented here. Single-crystal X-ray structure analysis shows that, in complex 1, the overall structure originates from the mucate-bridged gadolinium-based rectangular metallocycles. The packing view reveals the presence the two types of hydrophilic 1D channels filled with lattice water molecules, which are strongly hydrogen-bonded with coordinated water along the a and b axes, whereas for complex 2, the 3D framework originates from a carboxylate-bridged dysprosium-based criss-cross-type secondary building block. Magnetic studies reveal that 1 exhibits a significant magnetic entropy change (-ΔSM) of 30.6 J kg-1 K-1 for ΔH= 7 T at 3 K. Our electronic structure calculations under the framework of density functional theory reveal that exchange interactions between Gd3+ ions are weak and of the antiferromagnetic type. Complex 2 shows field-induced single-molecule-magnetic behavior. Impedance analysis shows that the proton conductivity of both complexes reaches up to the maximum value of 4.7 × 10-4 S cm-1 for 1 and 9.06 × 10-5 S cm-1 for 2 at high temperature (>75 °C) and relative humidity (RH; 95%). The Monte Carlo simulations confirm the exact location of the adsorbed water molecules in the framework after humidification (RH = 95%) for 1. Further, the results from computational simulation also reveal that the presence of a more dense arrangement of adsorbed water molecules through hydrogen bonding in a particular type of channel (along the a axis) contributes more to the proton migration compared to the other channel (along the b axis) in the framework.

Synthesis and physical properties of spin-1 honeycomb lattice Pb 6 Ni 9 (TeO 6 ) 5

Abstract We report the magnetic and dielectric properties of the spin-1 honeycomb lattice compound Pb6Ni9(TeO6)5. It crystallizes in hexagonal structure with a non-centrosymmetric space group P6322. DC magnetic susceptibility, AC magnetic susceptibility, and heat capacity studies reveal a magnetic long-range-order at TN≃24 K with a weak ferromagnetic component. The ground state is identified to be a canted antiferromagnetic type which is driven by the Dzyaloshinsky-Moriya interaction. A change in slope in the dielectric permittivity and a sudden drop in the loss tangent at TN implies the coupling of electric and magnetic order parameters.

Magnetic behavior of Bi5Nb3–3xFe3xO15–δ solid solutions

Most bismuth compounds with layered perovskite-like structure, analogs of Aurivillius phases, exhibit ferroelectric properties and are of interest from both practical and theoretical points of view. In this study, we carried out magnetochemical measurements of an electronic state and exchange interactions between iron atoms in the solid solutions Bi5Nb3O15, obtained by heterovalent substitution of niobium by atoms of iron (III). The iron-containing solid solutions were obtained in a narrow concentration range at x≤0.06. The iron-containing solid solutions at concentrations x> 0.005 are characterized by monoclinic distortion of the tetragonal cell (P2/m). The measurements of magnetic susceptibility of the solid solutions were carried out by the Faraday method in the temperature range of 77 - 400 K. The isotherms of a paramagnetic component of magnetic susceptibility of iron atoms are typical of antiferromagnets. The effective magnetic moment of single iron atoms increases with increasing temperature from 6.87 mB (90 K) to 6.92 mB (320 K). The study of the iron-containing Bi5Nb3O15 solid solutions has shown that, in the solid solutions iron (III) atoms aggregate to form dimers and tetramers with antiferromagnetic and ferromagnetic types of exchange. The values of antiferromagnetic and ferromagnetic exchange in dimers, Jdim = - 60 cm-1 and Jdim = 40 cm-1, and tetramers, Jtetr = - 40 cm-1 and Jtetr = 25 cm-1 correspondently.

Site preferences for La and Pr in Nd2Fe14B permanent magnet: A first principles study

Using the first principles method, we studied the site preference and the magnetic ground state of rare-earth elements La and Pr doped Nd2Fe14B permanent magnet. It was found that the La preferred the f-site doping at low doping ratio (12.5 %) while the g-site was more favorable at high doping (25 %). For the Pr impurity, we observed the opposite behavior because the site preference was switched. In addition, the spin configuration also depended on the impurity type and concentration. An antiferromagnetic (AFM) type spin configuration was found at both lower and higher doping ratios of La. For the Pr impurity, at a lower doping ratio, the AFM spin configuration was still preserved. However, the ferromagnetic spin configuration was more stable at a high doping ratio. Through impurity-substitution energy calculations, we found that the La impurity preferred to enter into the 2:14:1 phase at low doping, but it favored the grain-boundary phase at high (25 %) doping ratio. On the other hand, we observed that the Pr always preferred the main phase for both low and high doping concentrations.

Shaken not stirred: creating exotic angular momentum states by shaking an optical lattice

We propose a method to create higher orbital states of ultracold atoms in the Mott regime of an optical lattice. This is done by periodically modulating the position of the trap minima (known as shaking) and controlling the interference term of the lasers creating the lattice. These methods are combined with techniques of shortcuts to adiabaticity. As an example of this, we show specifically how to create an anti-ferromagnetic type ordering of angular momentum states of atoms. The specific pulse sequences are designed using Lewis–Riesenfeld invariants and a four-level model for each well. The results are compared with numerical simulations of the full Schrödinger equation.

Observation of weak ferromagnetism and the sizable magnetocaloric effect in Co2V2O7

The magnetic behavior of cobalt pyrovanadate compound Co2V2O7 with dichromate structure is reported. The compound undergoes long range magnetic ordering below TC=8K and our study identifies the ground state to be a canted antiferromagnetic type with a weak ferromagnetic component. The transition at TC is found to be first-order in nature as evident from the presence of distinct thermal hysteresis in the temperature dependent magnetization data. Below TC, a significantly large value of magnetic relaxation is observed which is possibly due to the metastability associated with the first order phase transition. Interestingly, the sample exhibits a sizable magneto-caloric effect around TC (∼4.1Jkg−1. K−1 for 50kOe of field change) which is reasonably high among antiferromagnetic transition metal oxides with weak ferromagnetism.

Chemically synthesized phase-pure BiFeO3 nanoparticles: Influence of agents on the purity

Single-phase BiFeO3 (BFO) nanoparticles with an average size of ∼64 nm were synthesized using formic acid and ethylene glycol as agents through a modified Pechini type sol–gel method. The present work highlights the synthesis of phase-pure BFO that lies on the right selection of chelating agent and complexing agent. Thermal and Fourier transform infrared (FTIR) studies revealed the temperature at which the metal oxide forms. X-ray diffraction patterns showed a gradual phase evolution as calcined temperature increased from 400 to 600 °C. The values of Rietveld refinement parameters (Rwp=5.42%, Rp=4.2%, Goodness of fit (S)=1.29) confirmed the single-phase BFO corresponding to rhombohedral perovskite structure with the space group R3c. Selected area electron diffraction pattern displayed the polycrystalline nature of the synthesized particles. The M–H loop measured at room temperature for the sample calcined at 500 °C revealed a ferromagnetic-like component with a coercivity of ∼907 Oe, whereas the sample calcined at 600 °C exhibited the typical antiferromagnetism.

Magnetic behavior of Gd3Ru4Al12, a layered compound with distorted kagomé net

The magnetic behavior of the compound, Gd3Ru4Al12, which was reported about two decades ago to crystallize in a hexagonal structure (space group P63/mmc), has not been investigated in the past literature despite interesting structural features (that is, magnetic layers and triangular as well as kagomé-lattice features favoring frustrated magnetism) characterizing this compound. We report here the results of studies of magnetization, heat capacity and magnetoresistance in the temperature range T = 1.8–300 K. The results establish that there is a long-range magnetic order of antiferromagnetic type below (TN =) 18.5 K, despite a much larger value (~80 K) of paramagnetic Curie temperature with a positive sign characteristic of ferromagnetic interaction. We attribute this to geometric frustration. The most interesting finding is that there is an additional magnetic anomaly below ~55 K before the onset of long-range order in the magnetic susceptibility data. Concurrent with this observation, the sign of isothermal change in entropy, ΔS = S(0) − S(H), where H is the externally applied magnetic field, remains positive above TN, with a broad peak. This observation indicates the presence of ferromagnetic clusters before the onset of long-range magnetic order. Thus, this compound may serve as an example of a situation in which magnetic frustration due to geometrical reasons faces competition from such magnetic precursor effects. There is also a reversal of the sign of −ΔS in the curves for lower final fields (H < 30 kOe) on entering the magnetically ordered state consistent with the entrance to an antiferromagetic state. The magnetoresistance behavior is consistent with the above conclusions.

Realization of two-dimensional ferromagnetism with giant coercivity in ultrathinβ−Ni(OH)2layers grown on aMoS2surface

Due to the charge transfer effect at the contact of transition metal (TM) and $\mathrm{Mo}{\mathrm{S}}_{2}$, the use of ferromagnets in $\mathrm{Mo}{\mathrm{S}}_{2}$ based spin transistor is not suitable. On the other hand, $\ensuremath{\beta}\text{\ensuremath{-}}\mathrm{Ni}{(\mathrm{OH})}_{2}$ is known to be a layered type material with antiparallel Ni spins in alternate layers. Here, an ultrathin layer of antiferromagnetic $\ensuremath{\beta}\text{\ensuremath{-}}\mathrm{Ni}{(\mathrm{OH})}_{2}$ is grown on the $\mathrm{Mo}{\mathrm{S}}_{2}$ surface to achieve complete ferromagnetism with giant coercivity (2925 Oe). The origin of this ferromagnetic ordering is the reduction of Ni spin moments in $\mathrm{Ni}{(\mathrm{OH})}_{2}$ layer adjacent to $\mathrm{Mo}{\mathrm{S}}_{2}$ surface due to charge transfer from S to Ni. The use of antiferromagnetic layered type material to achieve ferromagnetic ordering with giant coercivity is a new concept to realize perfect two-dimensional (2D) ferromagnets which have major advantages due to the huge change in coercivity with thickness.

Salicylic aldehyde and 2-N-tosylaminobenzaldehyde tetrazolyl hydrazones and their complexes

Tetrazolyl hydrazones of salicylic aldehyde and 2-N-tosylaminobenzaldehyde as well as zinc(II) and copper(II) complexes on their base have been prepared. Quantum-chemical simulation of tautomerism of the hydrazones in vacuum and in the solutions has been performed. IR and NMR spectroscopy and magnetochemistry studies have revealed that the complexes are mononuclear; however, weak intermolecular exchange interaction of the antiferromagnetic type has been detected in the copper(II) complexes.

Interface between an optically isotropic medium and a one-dimensional magnetoelectric photonic crystal as a controlled frequency-selective surface

The effect a constant external magnetic field has on the magnitude and direction of an energy flux carried by evanescent TM or TE wave in a two-component one-dimensional magnetic photonic crystal of the centroantisymmetric antiferromagnetic type (a nonmagnetic insulator) is investigated.

Constructing a magnetic handle for antiferromagnetic manganites

An intrinsic property of antiferromagnetic materials is the compensation of the magnetic moments from the individual atoms that prohibits the direct interaction of the spin lattice with an external magnetic field. To overcome this limitation we have created artificial spin structures by heteroepitaxy between two bulk antiferromagnets ${\mathrm{SrMnO}}_{3}$ and ${\mathrm{NdMnO}}_{3}$. Here, we demonstrate that charge transfer at the interface results in the creation of thin ferromagnetic layers adjacent to $A$-type antiferromagnetism in thick ${\mathrm{NdMnO}}_{3}$ layers. A novel interference based neutron diffraction technique and polarized neutron reflectometry are used to confirm the presence of ferromagnetism in the ${\mathrm{SrMnO}}_{3}$ layers and to probe the relative alignment of antiferromagnetic spins induced by the coupling at the ferro- to antiferromagnet interface. A density functional theory analysis of the driving forces for the exchange reveals strong ferromagnetic interfacial coupling through quantifiable short range charge transfer. These results confirm a layer-by-layer control of magnetic arrangements that constitutes a promising step on a path towards isothermal magnetic control of antiferromagnetic arrangements as would be necessary in spin-based heterostructures like multiferroic devices.